Ontology-mediated querying is an established subfield of knowledge
representation. The general aim is to enrich a database with an
ontology to add domain knowledge and to extend the vocabulary
available for query formulation
[1]}, [2]}, [3]}. Expressive
description logics (DLs) such as and are a popular choice
for the ontology language as they underpin the widely used OWL DL
profile of the OWL 2 ontology language. However, ontology-mediated
querying with these languages is coNP-complete in data
complexity even for simple atomic queries (AQs) of the form \(A(x)\) 
and thus scales poorly to larger amounts of data. One reaction to this
problem is to resort to approximate query answers, as done for example
in [4]}, [5]}. A
potential alternative is to only admit databases from a class that is
sufficiently restricted so that non-approximate answers can be
computed in , or to decompose the input database into component
databases from such a class.
